Back to EveryPatent.com
United States Patent |
5,014,624
|
Baxter
,   et al.
|
May 14, 1991
|
Discarding sabots
Abstract
A sabot for use with a spin stabilized projectile comprises a closed front
end portion having lines or strips of weakness running along sides of the
sabot which meet at a front end surface of the sabot, thereby providing a
continuously extending line or region of weakness across the front end
surface.
Preferably, the sabot front end portion has at least three, desirably four
or more, lines or strips of weakness running along the length of the front
end portion. These lines or strips may meet at an intersection of lines or
strips at the front end surface, but they preferably meet at a front end
membrane region.
Discarding sabots according to the present invention are especially
suitable for use with tubular projectiles. These projectiles may for
example be used in training ammunition rounds which are suitable for
firing from the UK 30 mm RARDEN (UK Registered Trade Mark) Gun.
Inventors:
|
Baxter; James E. (Cheshire, GB2);
Poole; Robert D. (Stoke-on-Trent, GB2)
|
Assignee:
|
Royal Ordnance plc (London, GB2)
|
Appl. No.:
|
300188 |
Filed:
|
January 23, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
102/503; 102/520; 102/523 |
Intern'l Class: |
F42B 010/34; F42B 014/06 |
Field of Search: |
102/503,513,520-523
|
References Cited
U.S. Patent Documents
3164092 | Jan., 1965 | Reed et al. | 102/522.
|
3446147 | May., 1969 | Engel et al. | 102/523.
|
3771458 | Nov., 1973 | Schweimler et al. | 102/523.
|
3951071 | Apr., 1976 | Germershausen | 102/523.
|
4000698 | Jan., 1977 | Corney | 102/522.
|
4249466 | Feb., 1981 | Rossmann et al. | 102/93.
|
4301736 | Nov., 1981 | Flatau et al. | 102/503.
|
4476785 | Oct., 1984 | Hoffman et al. | 102/522.
|
4735148 | Apr., 1988 | Holtzman et al. | 102/522.
|
Primary Examiner: Tudor; Harold J.
Attorney, Agent or Firm: Stevens, Davis, Miller & Mosher
Parent Case Text
This application is a continuation of application Ser. No. 135,249, filed
Dec. 21, 1987.
Claims
We claim:
1. A spin stabilised projectile assembly comprising a tubular projectile
and a discarding sabot mechanically engaged on and embracing the tubular
projectile to enclose the front end of the tubular projectile, said sabot
comprising a closed front end portion having elongate lateral zones of
weakness which meet at a front end surface of the sabot, thereby providing
a continuous zone of weakness extending across the front end surface and
joining together said elongate lateral zones to provide distinct fracture
lines along which the sabot will break into substantially equal-sized
petals.
2. An assembly as in claim 1 wherein the sabot front end portion has at
least three said elongate lateral zones of weakness running along the
length of the front end portion.
3. An assembly as in claim 1 wherein the elongate lateral zones of weakness
meet at a front end membrane region of the sabot.
4. An assembly as in claim 1 wherein the thickness of material of the sabot
front end portion along the elongate lateral zones of weakness is in the
range, 0.05 to 0.5 t, where t is the average thickness of the material in
the remainder of the front end portion.
5. An assembly as in claim 1 wherein the elongate lateral zones of weakness
are formed by grooves provided in a surface of the sabot, each of the
grooves comprising at least at its inner end, as seen in transverse
cross-section, a groove which is approximately V-shaped.
6. An assembly as in claim 1 wherein the sabot comprises a nose portion
which constitutes a separate component of the sabot.
7. An assembly as in claim 6 wherein the nose portion has inner and outer
surfaces each of which comprises at least one frusto-conical portion.
8. An assembly as in claim 1 wherein the tubular projectile has in
cross-section in a plane containing the longitudinal axis of the
projectile a front portion having an inner surface conically converging in
a direction facing toward the rear end of the projectile, an intermediate
portion having an inner surface of substantially constant diameter and a
rear portion having an inner surface conically diverging in a direction
facing toward the rear end of the projectile.
9. An assembly as in claim 8 wherein the tubular projectile incorporates a
tracer element embedded in a groove in the rear end wall of the tubular
projectile.
10. A discard sabot-projectile assembly, comprising:
a hollow tubular projectile having a substantially tubular shape; and
a sabot fitted to said projectile; and
wherein said tubular projectile has in a cross-section in a plane
containing a longitudinal axis of the projectile a front portion having an
inner surface conically converging toward the rear of the projectile, an
intermediate portion having an inner surface of substantially constant
diameter, and a rear portion having an inner surface conically diverging
toward the rear of the projectile; and
wherein said sabot comprises a front end portion having at least three
elongate longitudinal grooves, said grooves being V-shaped in transverse
cross-section at least at their bases, and said sabot further comprises a
membrane which closes at its front end, said grooves meeting at said
membrane thereby to form a continuous zone of weakness comprising said
grooves and said membrane, said continuous zone of weakness thus extending
laterally and over the front end of the sabot, and the thickness of the
material forming the sabot throughout the continuous zone of weakness
being in the range 0.05 t-1.5 t where t is the average thickness of the
material in the remainder of the front end portion of the sabot.
Description
The present invention relates to discarding sabots for projectiles.
It is well known in the design of projectiles fired from a gun for the
projectile to be provided as sub-calibre component which is used in
conjunction with a full calibre sabot. The sabot, which imparts the
propellant driving forces to the projectile on which it is fitted, is
designed to break and discard soon after exit from the muzzle of the gun,
leaving the projectile to travel towards its target.
Sabots used in conjunction with spin stabilised projectiles are
conventionally made of a lightweight material having a reasonably high
strength Such sabots normally include lines of weakness comprising break
grooves running along the sabot length which assist breaking and
discarding of the sabot after muzzle exit. In order to facilitate
manufacture of the sabot with break grooves, the front end of the sabot
normally comprises an open end or a solid portion which may be part of a
nose cap forming a component of the sabot.
We have found that the performance of such conventional sabots is not ideal
as described below.
We have now produced according to the present invention, a sabot
construction which is unexpectedly superior to the conventional sabot
constructions because it gives improved sabot performance in certain
applications without significantly increased difficulty of manufacture.
According to the present invention a sabot for use with a spin stabilised
projectile comprises a closed front end portion having lines or strips of
weakness running along sides of the sabot which meet at a front end
surface of the sabot, thereby providing a continuously extending line or
region of weakness across the front end surface.
Preferably, the sabot front end portion has at least three, desirably four
or more, lines or strips of weakness running along the length of the front
end portion. These lines or strips may meet at an intersection of lines or
strips at the front end surface, but they preferably meet at a front end
membrane region.
Desirably, the thickness of material of the sabot front end portion along
the lines or strips of weakness, including any membrane region where they
meet, is in the range 0.05 to 0.5 t, e.g. between 0.1 t and 0.4 t, where t
is the average thickness of the material in the remainder of the front end
portion, i.e. the average thickness of the main part of the front end. For
example, for a sabot of outer diameter of 25 mm to 30 mm, the average
thickness t may be in the range 2 mm to 8 mm and the thickness of the
lines or strips of weakness may be in the range 0.5 mm to 1.5 mm.
The lines or strips of weakness may be formed by grooves provided in the
inner or outer surface of the sabot or both. For example, where break
grooves are formed in the outer surface of the sabot the lines or strips
of weakness comprise the material remaining at the inner end of the
groove; The inner surface of the sabot may be continuous in the regions
where the grooves are formed in the outer surface. As in the prior art,
the break grooves may comprise at least at their inner end, as seen in
transverse cross-section, a groove which is approximately V-shaped.
The sabot may have an overall shape comprising substantially a right
circular cylindrical tube which includes a closed tapered nose portion at
its front. The nose portion may form a separate component of the sabot or
it may be an integral part thereof.
Preferably, the nose portion may comprise any suitable shape, e.g. an ogive
or a portion having a frustro-conical inner or outer surface or a portion
having an inner or outer surface or both which has a plurality of
frustro-conical portions of different cone angle. The thickness of the
side wall of the nose portion in regions other than the lines or strips of
weakness may vary along its length. Where the nose portion is a separate
sabot component, this side wall thickness may be reduced to substantially
the same thickness as that of the lines or strips of weakness at the rear
end of the nose portion.
Preferably, the nose portion has a front end having an outer diameter less
than one fifth of the outer diameter of the sabot side wall in the region
of its cylindrical tubular body. Preferably, the front end comprises a
border comprising an annulus or other suitable shape having radially
extending grooves therein and having in its non-grooved parts an average
thickness t substantially the same as the thickness of the side wall of
the sabot in the main part of its tubular body region and an inner
membrane having a thickness of from 0.05 t to 0.5 t, e.g. 0.1 t to 0.4 t,
formed by providing a recess in the front end in the region bounded by the
border.
The sabot according to the present invention may be made of any of the
materials conventionally used for production of discarding sabots and may
be made by manufacturing methods which are known per se. For example, the
sabot may be made of a lightweight polymeric material, e.g. a
thermoplastic such as nylon, polycarbonate, polyester, phenolics or
polyurethane or a thermosetting or cold setting polymer such as
polyurethane. The polymeric material may be reinforced, e.g. with fibres
such as glass, carbon, aramid, nylon, polyolefin or other known
reinforcing fibres. Alternatively, the sabot may be made of a high
strength lightweight alloy such as an aluminium or magnesium alloy.
Where the sabot according to the present invention is made from a polymeric
material it may be made by injection moulding, compression moulding or any
other suitable known process. The lines or strips of weakness and the
optional membrane may be formed in such a moulding process and/or may be
formed by subsequent machining.
Where the sabot according to the present invention is made from a metallic
material it may be cast or spun or extruded or machined. The lines or
strips or weakness and the optional membrane may be formed during this
process and/or by subsequent machining.
Discarding sabots according to the present invention are especially
suitable for use with tubular projectiles. These projectiles may for
example be used in training ammunition rounds which are suitable for
firing from the 30 mm RARDEN (UK Registered Trade Mark) Gun manufactured
by the present Applicant Company. Where a tubular projectile is used in
conjunction with a sabot according to the present invention the tubular
projectile preferably has in cross-section in a plane containing the
projectile axis a front portion having an inner surface conically
converging in a direction facing toward the rear end of the projectile, an
intermediate portion having an inner surface of substantially constant
diameter and a rear portion having an inner surface conically diverging in
a direction facing toward the rear end of the projectile. Such projectiles
may for example be of the form invented by Abraham Flatau and Joseph
Huerta as described in U.S. Pat. No. 1,571,010 assigned to the present
Applicant Company, Royal Ordnance plc.
Tubular projectiles used in conjunction with sabots according to the
present invention may incorporate a tracer element as described in
copending UK Patent Application No. 8,628,514 by the present Applicant
Company.
We have found that where discarding sabots are used with tubular
projectiles, it is highly desirable when the sabot breaks, to avoid the
formation of sabot pieces which might become lodged in the open front end
of the tubular projectile, thereby affecting the aerodynamic properties of
the projectile. We have demonstrated in firing trials involving high speed
photography, that prior art sabots which contain a solid front portion as
mentioned above can break in such a manner that pieces are formed which
might lodge in a tubular projectile. This problem may be overcome by the
use of known sabots having an open ended front portion, but such
open-ended sabots suffer from the disadvantage of lacking an environmental
barrier, e.g. to protect against the ingress of rainwater. The sabots
according to the present invention have been shown by firing trials
surprisingly to break cleanly into substantially equal sized petals which
discard laterally of the projectile. The closed front end of such sabots
provides a suitable environmental barrier.
Embodiments of the present invention will now be described by way of
example with reference to the accompanying drawings, in which:
FIG. 1 is a longitudinal cross-sectional view of a sabot embodying the
present invention.
FIG. 2 is an end view as seen at the front end of the sabot shown in FIG.
1.
FIG. 3 is a longitudinal cross-sectional view of a component of an
alternative sabot embodying the present invention.
FIG. 4 is a longitudinal cross-sectional view of a discard sabot-projectile
assembly in accordance with the invention comprising a tubular projectile
and a sabot similar to that of FIGS. 1 and 2.
In FIGS. 1 and 2 a sabot 1 comprises a circular cylindrical tubular body 3
having an open rear end 4 and a front nose portion 5 comprising a closed
front end 6. The nose portion 5 has an inner surface which comprises a
frustro-conical region 7 and a frustro-conical region 9 of increased cone
angle. The outer surface comprises a cylindrical region 8 and a
frustro-conical region 10, the nose portions has four equally spaced break
grooves 11 running along its length. The grooves 11 are parallel-sided
grooves which are seen in FIG. 2 to terminate in cross-section with an
approximate V-shape leaving a strip 13 (FIG. 1) at the end of the V-shape
i.e. formed adjacent to the inner surface of the sabot 1. The front end 6
of the sabot 1 comprises a membrane 15 of thickness similar to that of the
strips 13 at which the strips 13 meet. An annular border 17 of thicker
material, through which the grooves 11 pass, surrounds the membrane 15 at
the front end 6 as a continuation of the nose portion 5. The grooves 11
become shallow and eventually run out adjacent to the rear end 4.
In operation, the sabot 1 after exit from a gun muzzle (not shown) breaks
about its rear end which acts as a hinge, into four substantially equal
petals along the strips 13 which discard laterally relative to the axis of
the sabot 1.
FIG. 3 shows a nose cap 2 of an alternative sabot. In this case the sabot
comprises two parts, a substantially cylindrical body (not shown) and a
nose cap portion as shown in FIG. 3. Parts similar to those of the sabot 1
shown in FIGS. 1 and 2 are given like reference numerals. In the case of
FIG. 3, the break grooves 13 are V-shaped but do not contain a
parallel-sided section and the thickness of the nose cap 21 tapers toward
its rear end. The overall shape of the outer surface is similar to that of
the inner surface of the nose cap 21. Otherwise, the nose cap 21 has a
construction and operation similar to that of the front portion of the
sabot 1 of FIG. 1.
FIG. 4 illustrates a construction for launching a tubular projectile in
conjunction with a sabot embodying the present invention and for igniting
a tracer composition contained in the projectile rear end wall in the
manner described and claimed in UK Patent Application No. 8628514. The
projectile is indicated by reference numeral 31. The tracer composition of
the projectile 31 is indicated by reference numeral 33. A sabot 35 which
is of a form similar to that described above with reference to FIG. 1, is
fitted over the projectile 31. A driving band 37 is attached to the outer
surface of the sabot 35. A base pusher 39 carrying an obturator 38 is
located behind the rear surface of the projectile 31 and rear surfaces the
sabot 35 which include a circular recess into which a corresponding
portion 42 of the base pusher 39 fits. The pusher 39 has an annular
channel 41 extending therethrough in a direction parallel to the axes of
the pusher 39 and projectile 31. The channel 41 has three regions, namely
an annular recess 41a facing the tracer composition 33, a narrow portion
41b and a wider portion 41c behind the narrow portion 41b. The wider
portion 41c houses an annular septum 43.
In operation, the base pusher 39 is contained inside a gun in a
conventional launch cartridge (not shown) in front of a known gun
propellant (not shown). When the gun is fired the propellant is ignited
causing a rapid expansion of gas which is obturated by the obturator 38.
The pressure built up causes the projectile 31 and sabot 35 to be driven
by the pusher 39 in a forward direction out of the gun. The driving band
37 engages the rifling of the gun (not shown) to impart spin to the
projectile to maintain stability of the projectile in flight.
When the pressure of the hot propellant gas produced by the initiation of
the main propellant charge reaches a pre-determined limit the septum 43
bursts allowing the gas to enter the channel 41 and reach the tracer
composition 33 which it thereby ignites.
The narrow portion 41b allows this to be achieved without a build-up of
undesirable high gas pressure behind the projectile 31. It is desirable to
prevent such a build-up in order to prevent gas leakage on separation of
the projectile 31 from the pusher 39 before acceleration starts.
On leaving the muzzle of the gun the sabot 35 is rapidly discarded in the
manner described above with reference to FIGS. 1 and 2 allowing the
projectile 31 to proceed toward the target. The tracer composition allows
the trajectory of the projectile to be tracked in flight.
Top